1. Field of the Invention
This invention relates generally to gate-source structures for static induction transistors and more particularly to static induction transistors fabricated of silicon carbide.
2. Description of the Prior Art
Static induction transistors are field effect semiconductor devices capable of operation at relatively high frequency and power. The transistors are characterized by short, high resistivity semiconductor channel which may be controllably depleted of carriers. Static induction transistors generally use vertical geometry with source and drain electrodes placed on opposite sides of a thin, high resistivity layer of one conductivity type. Gate regions of opposite conductivity type are positioned in the high resistivity layer on opposite sides of the source electrode. During operation, a reverse bias is applied between the gate region and the remainder of the high resistivity layer causing a depletion region to extend into the channel below the source. As the magnitude of the reverse bias is varied, the source drain current and voltage derived from an attached energy source will also vary. Such devices are described in U.S. Pat. No. 4,713,358 to Bulat et al.
Silicon carbide is a wide energy band gap semiconductor (approximately 3 eV), and is thus an attractive material for the fabrication of integrated-power circuitry. Silicon carbide offers high saturation electron velocity (approximately 2.times.10.sup.7 cm/s), high junction breakdown voltage (approximately 2.times.10.sup.7 V/cm), high thermal conductivity (approximately 5 W/cm .degree.C.) and broad operating temperature range (around 1100.degree. C.). In addition, the energy band gap and thus the maximum operating temperature range of silicon carbide is at least twice that of conventional semiconductors.
Diffused junctions are not practical at the present time in silicon carbide based devices. Therefore, instead of the diffused p/n junction that has been used in silicon static induction transistors, other techniques must be developed to fabricate the gates in silicon carbide devices.